// Package sftpd implements the SSH File Transfer Protocol as described in https://tools.ietf.org/html/draft-ietf-secsh-filexfer-02.
// It uses pkg/sftp library:
// https://github.com/pkg/sftp
package sftpd

import (
	"context"
	"fmt"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"sync"
	"time"

	"github.com/drakkan/sftpgo/dataprovider"
	"github.com/drakkan/sftpgo/logger"
	"github.com/drakkan/sftpgo/metrics"
	"github.com/drakkan/sftpgo/utils"
)

const (
	logSender           = "sftpd"
	logSenderSCP        = "scp"
	logSenderSSH        = "ssh"
	uploadLogSender     = "Upload"
	downloadLogSender   = "Download"
	renameLogSender     = "Rename"
	rmdirLogSender      = "Rmdir"
	mkdirLogSender      = "Mkdir"
	symlinkLogSender    = "Symlink"
	removeLogSender     = "Remove"
	chownLogSender      = "Chown"
	chmodLogSender      = "Chmod"
	chtimesLogSender    = "Chtimes"
	sshCommandLogSender = "SSHCommand"
	operationDownload   = "download"
	operationUpload     = "upload"
	operationDelete     = "delete"
	operationRename     = "rename"
	operationSSHCmd     = "ssh_cmd"
	protocolSFTP        = "SFTP"
	protocolSCP         = "SCP"
	protocolSSH         = "SSH"
	handshakeTimeout    = 2 * time.Minute
)

const (
	uploadModeStandard = iota
	uploadModeAtomic
	uploadModeAtomicWithResume
)

var (
	mutex                sync.RWMutex
	openConnections      map[string]Connection
	activeTransfers      []*Transfer
	idleConnectionTicker *time.Ticker
	idleTimeout          time.Duration
	activeQuotaScans     []ActiveQuotaScan
	dataProvider         dataprovider.Provider
	actions              Actions
	uploadMode           int
	setstatMode          int
	supportedSSHCommands = []string{"scp", "md5sum", "sha1sum", "sha256sum", "sha384sum", "sha512sum", "cd", "pwd",
		"git-receive-pack", "git-upload-pack", "git-upload-archive", "rsync"}
	defaultSSHCommands = []string{"md5sum", "sha1sum", "cd", "pwd"}
	sshHashCommands    = []string{"md5sum", "sha1sum", "sha256sum", "sha384sum", "sha512sum"}
	systemCommands     = []string{"git-receive-pack", "git-upload-pack", "git-upload-archive", "rsync"}
)

type connectionTransfer struct {
	OperationType string `json:"operation_type"`
	StartTime     int64  `json:"start_time"`
	Size          int64  `json:"size"`
	LastActivity  int64  `json:"last_activity"`
	Path          string `json:"path"`
}

// ActiveQuotaScan defines an active quota scan
type ActiveQuotaScan struct {
	// Username to which the quota scan refers
	Username string `json:"username"`
	// quota scan start time as unix timestamp in milliseconds
	StartTime int64 `json:"start_time"`
}

// Actions to execute on SFTP create, download, delete and rename.
// An external command can be executed and/or an HTTP notification can be fired
type Actions struct {
	// Valid values are download, upload, delete, rename, ssh_cmd. Empty slice to disable
	ExecuteOn []string `json:"execute_on" mapstructure:"execute_on"`
	// Absolute path to the command to execute, empty to disable
	Command string `json:"command" mapstructure:"command"`
	// The URL to notify using an HTTP GET, empty to disable
	HTTPNotificationURL string `json:"http_notification_url" mapstructure:"http_notification_url"`
}

// ConnectionStatus status for an active connection
type ConnectionStatus struct {
	// Logged in username
	Username string `json:"username"`
	// Unique identifier for the connection
	ConnectionID string `json:"connection_id"`
	// client's version string
	ClientVersion string `json:"client_version"`
	// Remote address for this connection
	RemoteAddress string `json:"remote_address"`
	// Connection time as unix timestamp in milliseconds
	ConnectionTime int64 `json:"connection_time"`
	// Last activity as unix timestamp in milliseconds
	LastActivity int64 `json:"last_activity"`
	// Protocol for this connection: SFTP, SCP, SSH
	Protocol string `json:"protocol"`
	// active uploads/downloads
	Transfers []connectionTransfer `json:"active_transfers"`
	// for protocol SSH this is the issued command
	SSHCommand string `json:"ssh_command"`
}

type sshSubsystemExitStatus struct {
	Status uint32
}

type sshSubsystemExecMsg struct {
	Command string
}

func init() {
	openConnections = make(map[string]Connection)
	idleConnectionTicker = time.NewTicker(5 * time.Minute)
}

// GetDefaultSSHCommands returns the SSH commands enabled as default
func GetDefaultSSHCommands() []string {
	result := make([]string, len(defaultSSHCommands))
	copy(result, defaultSSHCommands)
	return result
}

// GetSupportedSSHCommands returns the supported SSH commands
func GetSupportedSSHCommands() []string {
	result := make([]string, len(supportedSSHCommands))
	copy(result, supportedSSHCommands)
	return result
}

// GetConnectionDuration returns the connection duration as string
func (c ConnectionStatus) GetConnectionDuration() string {
	elapsed := time.Since(utils.GetTimeFromMsecSinceEpoch(c.ConnectionTime))
	return utils.GetDurationAsString(elapsed)
}

// GetConnectionInfo returns connection info.
// Protocol,Client Version and RemoteAddress are returned.
// For SSH commands the issued command is returned too.
func (c ConnectionStatus) GetConnectionInfo() string {
	result := fmt.Sprintf("%v. Client: %#v From: %#v", c.Protocol, c.ClientVersion, c.RemoteAddress)
	if c.Protocol == protocolSSH && len(c.SSHCommand) > 0 {
		result += fmt.Sprintf(". Command: %#v", c.SSHCommand)
	}
	return result
}

// GetTransfersAsString returns the active transfers as string
func (c ConnectionStatus) GetTransfersAsString() string {
	result := ""
	for _, t := range c.Transfers {
		if len(result) > 0 {
			result += ". "
		}
		result += t.getConnectionTransferAsString()
	}
	return result
}

func (t connectionTransfer) getConnectionTransferAsString() string {
	result := ""
	if t.OperationType == operationUpload {
		result += "UL"
	} else {
		result += "DL"
	}
	result += fmt.Sprintf(" %#v ", t.Path)
	if t.Size > 0 {
		elapsed := time.Since(utils.GetTimeFromMsecSinceEpoch(t.StartTime))
		speed := float64(t.Size) / float64(utils.GetTimeAsMsSinceEpoch(time.Now())-t.StartTime)
		result += fmt.Sprintf("Size: %#v Elapsed: %#v Speed: \"%.1f KB/s\"", utils.ByteCountSI(t.Size),
			utils.GetDurationAsString(elapsed), speed)
	}
	return result
}

// SetDataProvider sets the data provider to use to authenticate users and to get/update their disk quota
func SetDataProvider(provider dataprovider.Provider) {
	dataProvider = provider
}

func getActiveSessions(username string) int {
	mutex.RLock()
	defer mutex.RUnlock()
	numSessions := 0
	for _, c := range openConnections {
		if c.User.Username == username {
			numSessions++
		}
	}
	return numSessions
}

// GetQuotaScans returns the active quota scans
func GetQuotaScans() []ActiveQuotaScan {
	mutex.RLock()
	defer mutex.RUnlock()
	scans := make([]ActiveQuotaScan, len(activeQuotaScans))
	copy(scans, activeQuotaScans)
	return scans
}

// AddQuotaScan add an user to the ones with active quota scans.
// Returns false if the user has a quota scan already running
func AddQuotaScan(username string) bool {
	mutex.Lock()
	defer mutex.Unlock()
	for _, s := range activeQuotaScans {
		if s.Username == username {
			return false
		}
	}
	activeQuotaScans = append(activeQuotaScans, ActiveQuotaScan{
		Username:  username,
		StartTime: utils.GetTimeAsMsSinceEpoch(time.Now()),
	})
	return true
}

// RemoveQuotaScan removes an user from the ones with active quota scans
func RemoveQuotaScan(username string) error {
	mutex.Lock()
	defer mutex.Unlock()
	var err error
	indexToRemove := -1
	for i, s := range activeQuotaScans {
		if s.Username == username {
			indexToRemove = i
			break
		}
	}
	if indexToRemove >= 0 {
		activeQuotaScans[indexToRemove] = activeQuotaScans[len(activeQuotaScans)-1]
		activeQuotaScans = activeQuotaScans[:len(activeQuotaScans)-1]
	} else {
		logger.Warn(logSender, "", "quota scan to remove not found for user: %v", username)
		err = fmt.Errorf("quota scan to remove not found for user: %v", username)
	}
	return err
}

// CloseActiveConnection closes an active SFTP connection.
// It returns true on success
func CloseActiveConnection(connectionID string) bool {
	result := false
	mutex.RLock()
	defer mutex.RUnlock()
	if c, ok := openConnections[connectionID]; ok {
		err := c.close()
		c.Log(logger.LevelDebug, logSender, "close connection requested, close err: %v", err)
		result = true
	}
	return result
}

// GetConnectionsStats returns stats for active connections
func GetConnectionsStats() []ConnectionStatus {
	mutex.RLock()
	defer mutex.RUnlock()
	stats := []ConnectionStatus{}
	for _, c := range openConnections {
		conn := ConnectionStatus{
			Username:       c.User.Username,
			ConnectionID:   c.ID,
			ClientVersion:  c.ClientVersion,
			RemoteAddress:  c.RemoteAddr.String(),
			ConnectionTime: utils.GetTimeAsMsSinceEpoch(c.StartTime),
			LastActivity:   utils.GetTimeAsMsSinceEpoch(c.lastActivity),
			Protocol:       c.protocol,
			Transfers:      []connectionTransfer{},
			SSHCommand:     c.command,
		}
		for _, t := range activeTransfers {
			if t.connectionID == c.ID {
				if t.lastActivity.UnixNano() > c.lastActivity.UnixNano() {
					conn.LastActivity = utils.GetTimeAsMsSinceEpoch(t.lastActivity)
				}
				var operationType string
				var size int64
				if t.transferType == transferUpload {
					operationType = operationUpload
					size = t.bytesReceived
				} else {
					operationType = operationDownload
					size = t.bytesSent
				}
				connTransfer := connectionTransfer{
					OperationType: operationType,
					StartTime:     utils.GetTimeAsMsSinceEpoch(t.start),
					Size:          size,
					LastActivity:  utils.GetTimeAsMsSinceEpoch(t.lastActivity),
					Path:          c.fs.GetRelativePath(t.path),
				}
				conn.Transfers = append(conn.Transfers, connTransfer)
			}
		}
		stats = append(stats, conn)
	}
	return stats
}

func startIdleTimer(maxIdleTime time.Duration) {
	idleTimeout = maxIdleTime
	go func() {
		for t := range idleConnectionTicker.C {
			logger.Debug(logSender, "", "idle connections check ticker %v", t)
			CheckIdleConnections()
		}
	}()
}

// CheckIdleConnections disconnects clients idle for too long, based on IdleTimeout setting
func CheckIdleConnections() {
	mutex.RLock()
	defer mutex.RUnlock()
	for _, c := range openConnections {
		idleTime := time.Since(c.lastActivity)
		for _, t := range activeTransfers {
			if t.connectionID == c.ID {
				transferIdleTime := time.Since(t.lastActivity)
				if transferIdleTime < idleTime {
					c.Log(logger.LevelDebug, logSender, "idle time: %v setted to transfer idle time: %v",
						idleTime, transferIdleTime)
					idleTime = transferIdleTime
				}
			}
		}
		if idleTime > idleTimeout {
			err := c.close()
			c.Log(logger.LevelInfo, logSender, "close idle connection, idle time: %v, close error: %v", idleTime, err)
		}
	}
	logger.Debug(logSender, "", "check idle connections ended")
}

func addConnection(c Connection) {
	mutex.Lock()
	defer mutex.Unlock()
	openConnections[c.ID] = c
	metrics.UpdateActiveConnectionsSize(len(openConnections))
	c.Log(logger.LevelDebug, logSender, "connection added, num open connections: %v", len(openConnections))
}

func removeConnection(c Connection) {
	mutex.Lock()
	defer mutex.Unlock()
	delete(openConnections, c.ID)
	metrics.UpdateActiveConnectionsSize(len(openConnections))
	// we have finished to send data here and most of the time the underlying network connection
	// is already closed. Sometime a client can still be reading the last sended data, so we set
	// a deadline instead of directly closing the network connection.
	// Setting a deadline on an already closed connection has no effect.
	// We only need to ensure that a connection will not remain indefinitely open and so the
	// underlying file descriptor is not released.
	// This should protect us against buggy clients and edge cases.
	c.netConn.SetDeadline(time.Now().Add(2 * time.Minute))
	c.Log(logger.LevelDebug, logSender, "connection removed, num open connections: %v", len(openConnections))
}

func addTransfer(transfer *Transfer) {
	mutex.Lock()
	defer mutex.Unlock()
	activeTransfers = append(activeTransfers, transfer)
}

func removeTransfer(transfer *Transfer) error {
	mutex.Lock()
	defer mutex.Unlock()
	var err error
	indexToRemove := -1
	for i, v := range activeTransfers {
		if v == transfer {
			indexToRemove = i
			break
		}
	}
	if indexToRemove >= 0 {
		activeTransfers[indexToRemove] = activeTransfers[len(activeTransfers)-1]
		activeTransfers = activeTransfers[:len(activeTransfers)-1]
	} else {
		logger.Warn(logSender, transfer.connectionID, "transfer to remove not found!")
		err = fmt.Errorf("transfer to remove not found")
	}
	return err
}

func updateConnectionActivity(id string) {
	mutex.Lock()
	defer mutex.Unlock()
	if c, ok := openConnections[id]; ok {
		c.lastActivity = time.Now()
		openConnections[id] = c
	}
}

func isAtomicUploadEnabled() bool {
	return uploadMode == uploadModeAtomic || uploadMode == uploadModeAtomicWithResume
}

func executeNotificationCommand(operation, username, path, target, sshCmd, fileSize, isLocalFile string) error {
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()
	cmd := exec.CommandContext(ctx, actions.Command, operation, username, path, target, sshCmd)
	cmd.Env = append(os.Environ(),
		fmt.Sprintf("SFTPGO_ACTION=%v", operation),
		fmt.Sprintf("SFTPGO_ACTION_USERNAME=%v", username),
		fmt.Sprintf("SFTPGO_ACTION_PATH=%v", path),
		fmt.Sprintf("SFTPGO_ACTION_TARGET=%v", target),
		fmt.Sprintf("SFTPGO_ACTION_SSH_CMD=%v", sshCmd),
		fmt.Sprintf("SFTPGO_ACTION_FILE_SIZE=%v", fileSize),
		fmt.Sprintf("SFTPGO_ACTION_LOCAL_FILE=%v", isLocalFile),
	)
	startTime := time.Now()
	err := cmd.Run()
	logger.Debug(logSender, "", "executed command %#v with arguments: %#v, %#v, %#v, %#v, %#v, elapsed: %v, error: %v",
		actions.Command, operation, username, path, target, sshCmd, time.Since(startTime), err)
	return err
}

// executed in a goroutine
func executeAction(operation, username, path, target, sshCmd string, fileSize int64, isLocalFile bool) error {
	if !utils.IsStringInSlice(operation, actions.ExecuteOn) {
		return nil
	}
	var err error
	size := ""
	if fileSize > 0 {
		size = fmt.Sprintf("%v", fileSize)
	}
	if len(actions.Command) > 0 && filepath.IsAbs(actions.Command) {
		// we are in a goroutine but if we have to send an HTTP notification we don't want to wait for the
		// end of the command
		if len(actions.HTTPNotificationURL) > 0 {
			go executeNotificationCommand(operation, username, path, target, sshCmd, size, fmt.Sprintf("%t", isLocalFile))
		} else {
			err = executeNotificationCommand(operation, username, path, target, sshCmd, size, fmt.Sprintf("%t", isLocalFile))
		}
	}
	if len(actions.HTTPNotificationURL) > 0 {
		var url *url.URL
		url, err = url.Parse(actions.HTTPNotificationURL)
		if err == nil {
			q := url.Query()
			q.Add("action", operation)
			q.Add("username", username)
			q.Add("path", path)
			if len(target) > 0 {
				q.Add("target_path", target)
			}
			if len(sshCmd) > 0 {
				q.Add("ssh_cmd", sshCmd)
			}
			if len(size) > 0 {
				q.Add("file_size", size)
			}
			q.Add("local_file", fmt.Sprintf("%t", isLocalFile))
			url.RawQuery = q.Encode()
			startTime := time.Now()
			httpClient := &http.Client{
				Timeout: 15 * time.Second,
			}
			resp, err := httpClient.Get(url.String())
			respCode := 0
			if err == nil {
				respCode = resp.StatusCode
				resp.Body.Close()
			}
			logger.Debug(logSender, "", "notified operation %#v to URL: %v status code: %v, elapsed: %v err: %v",
				operation, url.String(), respCode, time.Since(startTime), err)
		} else {
			logger.Warn(logSender, "", "Invalid http_notification_url %#v for operation %#v: %v", actions.HTTPNotificationURL,
				operation, err)
		}
	}
	return err
}